This invention relates to combine harvesters and has particular reference to the air screen devices of such machines through which air is taken to effect cooling of an engine coolant or of a transmission fluid, for example.
While the terms "grain", "straw", and "tailings" are used principally throughout this specification for convenience, it should be understood that these terms are not intended to be limiting. Thus "grain" refers to that part of the crop which is threshed and separated from the discardable part of the crop material which is referred to as "straw". Incompletely threshed ears are referred to as "tailings".
The flow of air through the perforated air screen brings with it dust, chaff and other foreign matter which is present in abundance around a combine harvester during operation thereof and which settles on the outer surface of the screen. This foreign matter has to be removed from the outer surface of the air screen otherwise it soon blocks the latter thus impairing the cooling of the coolant, transmission fluid or other item being cooled. To this end, it is well known to mount the air screen for rotation and to provide within the air screen an impervious stationary member which serves to prevent the flow of air through successive portions of the air screen as it rotates past the stationary member. The foreign matter on the air screen portion rendered temporarily imperforate by the stationary member at a given instant falls from that portion under gravity and centrifugal forces. It is important that the foreign matter falls clear of the air screen as quickly as possible otherwise there is a distinct likelihood of the foreign matter being sucked back onto the air screen.
In certain instances, it is necessary, for reasons of other design considerations, to mount the air screen relatively close to a generally horizontal surface of the machine, whereby the requirement for the released foreign matter to clear the air screen area as soon as possible is not met. Thus the foreign matter tends to recirculate and furthermore, the generally horizontal surface of the machine acts as a resting place for pieces of straw or other discardable crop material which inevitably swirls around a combine harvester during operation, these pieces of straw often building up to an extent that the air screen is obscured in one or more places. Furthermore, this straw gives rise to a fire hazard since the air screen is in the vicinity of the engine.